As means for preventing a contact or collision between airplanes on the ground, there has been proposed an airplane ground guidance system in which a taxiway is divided into several continuous sections having a certain length, for example, about 100 m, an airplane-detecting apparatus is arranged in each control section and a subsequent airplane is prevented from advancing in a control section in which an airplane is already present (see Report of Investigation of Airplane Guidance System in Taxiways and Aprons of New Tokyo International Air Port, 1969-1975, by Aviation Promotion Foundation).
According to this system, one rectangular coil loop in which the length of the side parallel to the direction of advance of an airplane is much shorter than the airplane length, for example, 3 to 5 m, is arranged on each of inlet and exit sides of each control section so that the distance between the loop coils on inlet and exit sides is about 90 to about 100 m, the change of the self-inductance caused on passage of an airplane through the loop coil on the inlet side is detected by a sensor and a memory is brought into the set state by a signal of the sensor, whereby an advance-inhibiting lamp indicating the presence of an airplane in the control section is lighted to inhibit a subsequent airplane from advancing in this control section.
When the above-mentioned airplane which has advanced into the control section passes through the loop coil on the exit side, the memory in the set state is reset by an output signal from a corresponding sensor and an advance-admitting lamp indicating the absence of an airplane is lighted, whereby a subsequent airplane is allowed to advance into the control section.
Namely, occurrence of a contact or collision accident on the ground is prevented by allowing only one airplane to be present in one control section
Not only airplanes but also various automobiles such as passenger-transporting buses and maintenance vehicles run on the taxiway, and the change of the self-inductance is caused in the loop coil by passage of such a vehicle and a detection output is generated in the airplane-detecting apparatus. Moreover, these automobiles do not always run just on the taxiway but they often cross the taxiway, and there is a good possibility that automobiles pass only on one loop coil on the inlet or exit side.
In this case, in the above-mentioned guidance system in which the memory is set and reset, for example, when an automobile passes on the loop coil on the inlet side even into the absence of an airplane in the control section, the memory is set, and if the memory is not reset, a subsequent airplane is not allowed to advance in the control section. On the other hand, if an automobile passes on the loop coil on the exit side, since the memory into the set state is reset, the advance-admitting lamp is lighted even in the presence of an airplane in the control section, there is a risk of advance of subsequent airplane in the control section. Furthermore, in this control system, the control is established even in case of an automobile which is much smaller than an airplane, and it happens that the control section is occupied by one automobile and the operation efficiency of the taxiway si drastically reduced.
It is a primary object of the present invention to obviate the disadvantages of the above-mentioned system and provide an airplane guidance system in which an airplane is continuously detected in control sections of a taxiway for airplanes, an airplane is discriminated from an automobile by generating different detection patterns and guidance of an airplane is performed safely at a high efficiency.